Fix endpoint mode in Compose format.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

compose/loader/full-example.yml

@@ -1,4 +1,4 @@
-version: "3"
+version: "3.2"
 
 services:
   foo:
@@ -45,6 +45,7 @@ services:
         window: 120s
       placement:
         constraints: [node=foo]
+      endpoint_mode: dnsrr
 
     devices:
       - "/dev/ttyUSB0:/dev/ttyUSB0"

compose/loader/loader.go

@@ -220,9 +220,7 @@ func transform(source map[string]interface{}, target interface{}) error {
 	if err != nil {
 		return err
 	}
-	err = decoder.Decode(source)
-	// TODO: log unused keys
-	return err
+	return decoder.Decode(source)
 }
 
 func transformHook(

compose/loader/loader_test.go

@@ -674,6 +674,7 @@ func TestFullExample(t *testing.T) {
 			Placement: types.Placement{
 				Constraints: []string{"node=foo"},
 			},
+			EndpointMode: "dnsrr",
 		},
 		Devices:    []string{"/dev/ttyUSB0:/dev/ttyUSB0"},
 		DNS:        []string{"8.8.8.8", "9.9.9.9"},

compose/types/types.go

@@ -158,7 +158,7 @@ type DeployConfig struct {
 	Resources     Resources
 	RestartPolicy *RestartPolicy `mapstructure:"restart_policy"`
 	Placement     Placement
-	EndpointMode  string
+	EndpointMode  string `mapstructure:"endpoint_mode"`
 }
 
 // HealthCheckConfig the healthcheck configuration for a service